Cyclic olefin compositions for temporary wafer bonding

ABSTRACT

New compositions and methods of using those compositions as bonding compositions are provided. The compositions comprise a cycloolefin copolymer dispersed or dissolved in a solvent system, and can be used to bond an active wafer to a carrier wafer or substrate to assist in protecting the active wafer and its active sites during subsequent processing and handling. The compositions form bonding layers that are chemically and thermally resistant, but that can also be softened or dissolved to allow the wafers to slide or be pulled apart at the appropriate stage in the fabrication process.

GOVERNMENT FUNDING

This invention was made with government support under contract numberFA8650-05-D-5807 awarded by the Air Force Research Laboratory (AFRL).The United States Government has certain rights in the invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is broadly concerned with novel compositions andmethods of using those compositions to form bonding compositions thatcan support active wafers on a carrier wafer or substrate during waferthinning and other processing.

2. Description of the Prior Art

Wafer (substrate) thinning has been used to dissipate heat and aid inthe electrical operation of integrated circuits (IC). Thick substratescause an increase in capacitance, requiring thicker transmission lines,and, in turn, a larger IC footprint. Substrate thinning increasesimpedance while capacitance decreases impedance, causing a reduction intransmission line thickness, and, in turn, a reduction in IC size. Thus,substrate thinning facilitates IC miniaturization.

Geometrical limitations are an additional incentive for substratethinning. Via holes are etched on the backside of a substrate tofacilitate frontside contacts. In order to construct a via using commondry-etch techniques, geometric restrictions apply. For substratethicknesses of less than 100 μm, a via having a diameter of 30-70 μm isconstructed using dry-etch methods that produce minimal post-etchresidue within an acceptable time. For thick substrates, vias withlarger diameters are needed. This requires longer dry-etch times andproduces larger quantities of post-etch residue, thus significantlyreducing throughput. Larger vias also require larger quantities ofmetallization, which is more costly. Therefore, for backside processing,thin substrates can be processed more quickly and at lower cost.

Thin substrates are also more easily cut and scribed into ICs. Thinnersubstrates have a smaller amount of material to penetrate and cut andtherefore require less effort. No matter what method (sawing, scribe andbreak, or laser ablation) is used, ICs are easier to cut from thinnersubstrates. Most semiconductor wafers are thinned after frontsideoperations. For ease of handling, wafers are processed (i.e., frontsidedevices) at their normal full-size thicknesses, e.g., 600-700 μm. Oncecompleted, they are thinned to thicknesses of 100-150 μm. In some cases(e.g., when hybrid substrates such as gallium arsenide (GaAs) are usedfor high-power devices) thicknesses may be taken down to 25 μm.

Mechanical substrate thinning is performed by bringing the wafer surfaceinto contact with a hard and flat rotating horizontal platter thatcontains a liquid slurry. The slurry may contain abrasive media alongwith chemical etchants such as ammonia, fluoride, or combinationsthereof. The abrasive provides “gross” substrate removal, i.e.,thinning, while the etchant chemistry facilitates “polishing” at thesubmicron level. The wafer is maintained in contact with the media untilan amount of substrate has been removed to achieve a targeted thickness.

For a wafer thickness of 300 μm or greater, the wafer is held in placewith tooling that utilizes a vacuum chuck or some means of mechanicalattachment. When wafer thickness is reduced to less than 300 μm, itbecomes difficult or impossible to maintain control with regard toattachment and handling of the wafer during further thinning andprocessing. In some cases, mechanical devices may be made to attach andhold onto thinned wafers, however, they are subject to many problems,especially when processes may vary. For this reason, the wafers(“active” wafers) are mounted onto a separate rigid (carrier) substrateor wafer. This substrate becomes the holding platform for furtherthinning and post-thinning processing. Carrier substrates are composedof materials such as sapphire, quartz, certain glasses, and silicon, andusually exhibit a thickness of 1000 μm. Substrate choice will depend onhow closely matched the coefficient of thermal expansion (CTE) isbetween each material. However, most of the currently available adhesionmethods do not have adequate thermal or mechanical stability towithstand the high temperatures encountered in backside processingsteps, such as metallization or dielectric deposition and annealing.Many current methods also have poor planarity (which contributesexcessive total thickness variation across the wafer dimensions), andpoor chemical resistance.

One method that has been used to mount an active wafer to a carriersubstrate is via a thermal release adhesive tape. This process has twomajor shortcomings. First, the tapes have limited thickness uniformityacross the active wafer/carrier substrate interface, and this limiteduniformity is often inadequate for ultra-thin wafer handling. Second,the thermal release adhesive softens at such low temperatures that thebonded wafer/carrier substrate stack cannot withstand many typical waferprocessing steps that are carried out at higher temperatures.

Thermally stable adhesives, on the other hand, often require excessivelyhigh bonding pressures or bonding temperatures to achieve sufficientmelt flow for good bond formation to occur. Likewise, too muchmechanical force may be needed to separate the active wafer and carrierwafer because the adhesive viscosity remains too high at practicaldebonding temperatures. Thermally stable adhesives can also be difficultto remove without leaving residues.

There is a need for new compositions and methods of adhering an activewafer to a carrier substrate that can endure high processingtemperatures and that allow for ready separation of the wafer andsubstrate at the appropriate stage of the process.

SUMMARY OF THE INVENTION

The present invention overcomes the problems of the prior art by broadlyproviding a wafer bonding method, which includes providing a stackcomprising first and second substrates bonded together via a bondinglayer, and separating the first and second substrates. The bonding layeris formed from a composition comprising a cycloolefin copolymer (COC)dissolved or dispersed in a solvent system.

The invention also provides an article comprising first and secondsubstrates and a bonding layer. The first substrate comprises a backsurface and an active surface, which comprises at least one active siteand a plurality of topographical features. The second substrate has abonding surface. The bonding layer is bonded to the active surface ofthe first substrate and to the bonding surface of the second substrate.The bonding layer is formed from a composition comprising a cycloolefincopolymer dissolved or dispersed in a solvent system.

In a further embodiment, the invention is concerned with a compositionuseful for bonding two substrates together. The inventive compositioncomprises a cycloolefin copolymer and an ingredient dissolved ordispersed in a solvent system. The ingredient is selected from the groupconsisting of tackifier resins, low molecular weight cycloolefincopolymers, and mixtures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. (FIG.) 1 illustrates the inventive method of thinning and debondingtwo wafers according to the present invention;

FIG. 2 is a flow diagram showing the typical process steps followed inthe examples;

FIG. 3 is a graph depicting the rheological analysis results of bondingcompositions according to the invention debonded at 150° C.:

FIG. 4 is a graph depicting the rheological analysis results for bondingcompositions according to the invention debonded at 200° C.; and

FIG. 5 is a graph depicting the rheological analysis results for bondingcompositions according to the invention debonded at 250° C.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In more detail, the inventive compositions comprise a cycloolefincopolymer (COC) dispersed or dissolved in a solvent system. Thecopolymer is preferably present in the composition at levels of fromabout 5% to about 85% by weight, more preferably from about 5% to about60% by weight, and most preferably from about 10% to about 40% byweight, based upon the total weight of the composition taken as 100% byweight.

The nreferred copolymers are thermoplastic and preferably have a weightaverage molecular weight (M_(w)) of from about 2,000 Daltons to about200,000 Daltons, and more preferably from about 5,000 Daltons to about100,000 Daltons. Preferred copolymers preferably have a softeningtemperature (melt viscosity at 3,000 Pa·S) of at least about 100° C.,more preferably at least about 140° C., and even more preferably fromabout 160° C. to about 220° C. Suitable copolymers also preferably havea glass transition temperature (T_(g)) of at least about 60° C., morepreferably from about 60° C. to about 200° C., and most preferably fromabout 75° C. to about 160° C.

Preferred cycloolefin copolymers are comprised of recurring monomers ofcyclic olefins and acyclic olefins, or ring-opening polymers based oncyclic olefins. Suitable cyclic olefins for use in the present inventionare selected from the group consisting of norbornene-based olefins,tetracyclododecene-based olefins, dicyclonentadiene-based olefins, andderivatives thereof. Derivatives include alkyl (preferably C₁-C₂₀alkyls, more preferably C₁-C₁₀ alkyls), alkylidene (preferably C₁-C₂₀alkylidenes, more preferably C₁-C₁₀ alkylidenes), aralkyl (preferablyC₆-C₃₀ aralkyls, more preferably C₆-C₁₈ aralkyls), cycloalkyl(preferably C₃-C₃₀ cycloalkyls, more preferably C₃-C₁₈ cycloalkyls),ether, acetyl, aromatic, ester, hydroxy, alkoxy, cyano, amide, imide,and silyl-substituted derivatives. Particularly preferred cyclic olefinsfor use in the present invention include those selected from the groupconsisting of

and combinations of the foregoing, where each R₁ and R₂ is individuallyselected from the group consisting of —H, and alkyl groups (preferablyC₁-C₂₀ alkyls, more preferably C₁-C₁₀ alkyls), and each R₃ isindividually selected from the group consisting of —H, substituted andunsubstituted aryl groups (preferably C₆-C₁₈ aryls), alkyl groups(preferably C₁-C₂₀ alkyls, more preferably C₁-C₁₀ alkyls), cycloalkylgroups (preferably C₃-C₃₀ cycloalkyl groups, more preferably C₃-C₁₈cycloalkyl groups), aralkyl groups (preferably C₆-C₃₀ aralkyls, morepreferably C₆-C₁₈ aralkyl groups such as benzyl, phenethyl, andphenylpropyl, etc.), ester groups, ether groups, acetyl groups, alcohols(preferably C₁-C₁₀ alcohols), aldehyde groups, ketones, nitriles, andcombinations thereof.

Preferred acyclic olefins are selected from the group consisting ofbranched and unbranched C₂-C₂₀ alkenes (preferably C₂-C₁₀ alkenes). Morepreferably, suitable acyclic olefins for use in the present inventionhave the structure

where each R₄ is individually selected from the group consisting of —Hand alkyl groups (preferably C₁-C₂₀ alkyls, more preferably C₁-C₁₀alkyls). Particularly preferred acyclic olefins for use in the presentinvention include those selected from the group consisting of ethene,propene, and butene, with ethene being the most preferred.

Methods of producing cycloolefin copolymers are known in the art. Forexample, cycloolefin copolymers can be produced by chain polymerizationof a cyclic monomer with an acyclic monomer (such as norbornene withethene as shown below).

The reaction shown above results in an ethene-norbornene copolymercontaining alternating norbornanediyl and ethylene units. Examples ofcopolymers produced by this method include TOPAS®, produced byGoodfellow Corporation and TOPAS Advanced Polymers, and APEL®, producedby Mitsui Chemicals. A suitable method for making these copolymers isdisclosed in U.S. Pat. No. 6,008,298, incorporated by reference herein.

Cycloolefin copolymers can also be produced by ring-opening metathesispolymerization of various cyclic monomers followed by hydrogenation asillustrated below.

The polymers resulting from this type of polymerization can be thoughtof conceptually as a copolymer of ethene and a cyclic olefin monomer(such as alternating units of ethylene and cyclopentane-1,3-diyl asshown below).

Examples of copolymers produced by this method include ZEONOR® from ZeonChemicals, and ARTON® from JSR Corporation. A suitable method of makingthese copolymers is disclosed in U.S. Pat. No. 5,191,026, incorporatedby reference herein.

Accordingly, copolymers of the present invention preferably compriserecurring monomers of:

and combinations or the foregoing, where:

-   -   each R₁ and R₂ is individually selected from the group        consisting of —H, and alkyl groups (preferably C₁-C₂₀ alkyls,        more preferably C₁-C₁₀ alkyls), and    -   each R₃ is individually selected from the group consisting of        —H, substituted and unsubstituted aryl groups (preferably C₆-C₁₈        aryls), alkyl groups (preferably C₁-C₂₀ alkyls, more preferably        C₁-C₁₀ alkyls), cycloalkyl groups (preferably C₃-C₃₀ cycloalkyl        groups, more preferably C₃-C₁₈ cycloalkyl groups), aralkyl        groups (preferably C₆-C₃₀ aralkyls, more preferably C₆-C₁₈        aralkyl groups, such as benzyl, phenethyl, and phenylpropyl,        etc.), ester groups, ether groups, acetyl groups, alcohols        (preferably C₁-C₁₀ alcohols), aldehyde groups, ketones,        nitriles, and combinations thereof;        and

-   -   where:        -   is a single or double-bond; and        -   each R₄ is individually selected from the group consisting            of —H and alkyl groups (preferably C₁-C₂₀ alkyls, more            preferably C₁-C₁₀ alkyls).

The ratio of monomer (I) to monomer (II) within the polymer ispreferably from about 5:95 to about 95:5, and more preferably from about30:70 to about 70:30.

The inventive compositions are formed by simply mixing the cycloolefincopolymer and any other ingredients with the solvent system, preferablyat room temperature to about 150° C., for time periods of from about1-72 hours.

The composition should comprise at least about 15% by weight solventsystem, preferably from about 30% to about 95% by weight solvent system,more preferably from about 40% to about 90% by weight solvent system,and even more preferably from about 60% to about 90% by weight solventsystem, based upon the total weight of the composition taken as 100% byweight. The solvent system should have a boiling point of from about50-280° C., and preferably from about 120-250° C. Suitable solventsinclude, but are not limited to, methyl ethyl ketone (MEK) andcyclopentanone, as well as hydrocarbon solvents selected from the groupconsisting of limonene, mesitylene, dipentene, pinene, bicyclohexyl,cyclododecene, 1-tert-butyl-3,5-dimethylbenzene, butylcyclohexane,cyclooctane, cycloheptane, cyclohexane, methylcyclohexane, and mixturesthereof.

The total solids level in the composition should be at least about 5% byweight, preferably from about 5% to about 85% by weight, more preferablyfrom about 5% to about 60% by weight, and even more preferably fromabout 10% to about 40% by weight, based upon the total weight of thecomposition taken as 100% by weight.

According to the invention, the composition can include additionalingredients, including low molecular weight cyclooletin copolymer (COC)resins and/or tackifier resins or rosins. The composition can alsoinclude a number of optional ingredients selected from the groupconsisting of plasticizers, antioxidants, and mixtures thereof.

When a low molecular weight COC resin is used in the composition, it ispreferably present in the composition at a level of from about 2% toabout 80% by weight, more preferably from about 5% to about 50% byweight, and even more preferably from about 15% to about 35% by weight,based upon the total weight of the composition taken as 100% by weight.The term “low molecular weight cycloolefin copolymer” is intended torefer to COCs having a weight average molecular weight (M_(w)) of lessthan about 50,000 Daltons, preferably less than about 20,000 Daltons,and more preferably from about 500 to about 10,000 Daltons. Suchcopolymers also preferably have a T_(g) of from about 50° C. to about120° C., more preferably from about 60° C. to about 90° C., and mostpreferably from about 60° C. to about 70° C. Exemplary low molecularweight COC resins for use in the present compositions are those soldunder the name TOPAS® Toner™ (M_(w) 8,000), available from TopasAdvanced Polymers.

When a tackifier or rosin is utilized, it is preferably present in thecomposition at a level of from about 2% to about 80% by weight, morepreferably from about 5% to about 50% by weight, and even morepreferably from about 15% to about 35% by weight, based upon the totalweight of the composition taken as 100% by weight. The tackifiers arechosen from those having compatible chemistry with the cycloolefincopolymers so that no phase separation occurs in the compositions.Examples of suitable tackifiers include, but are not limited to,polyterpene resins (sold under the name SYLVARES™ TR resin; ArizonaChemical), beta-polyterpene resins (sold under the name SYLVARES™ TR-Bresin; Arizona Chemrical), styrenated terpene resins (sold under thename ZONATAC NG resin; Arizona Chemical), polymerized rosin resins (soldunder the name SYLVAROS® PR resin; Arizona Chemical), rosin ester resins(sold under the name EASTOTAC™ resin; Eastman Chemical), cyclo-aliphatichydrocarbon resins (sold under the name PLASTOLYN™ resin; EastmanChemical, or under the name ARKON™ resin; Arakawa Chemical), C5aliphatic hydrocarbon resins (sold under the name PICCOTAC™ resin;Eastman Chemical), hydrogenated hydrocarbon resins (sold under the nameREGALITE™ resin; Eastman Chemical), and mixtures thereof.

When an antioxidant is utilized, it is preferably present in thecomposition at a level of from about 0.1% to about 2% by weight, andmore preferably from about 0.5% to about 1.5% by weight, based upon thetotal weight of the composition taken as 100% by weight. Examples ofsuitable antioxidants include those selected from the group consistingof phenolic antioxidants (such as pentaerythritoltetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate sold under thename IRGANOX™ 1010 by Ciba), phosphite antioxidants (such astris(2,4-ditert-butylphenyl) phosphite sold under the name IRGAFOS™ 168by Ciba), phosphonite antioxidants (such astetrakis(2,4-di-tert-butylphenyl)[1,1-biphenyl]-4,4′-diylbisphosphonitesold under the name IRGAFOX® P-EPQ by Ciba), and mixtures thereof.

In alternative embodiments, it is preferred that the compositions areessentially free (less than about 0.1% and preferably about 0% byweight) of adhesion promoting agents, such asbis(trimethoxysilylethyl)benzene, aminopropyl tri(alkoxy silanes) (e.g.,aminopropyl tri(methoxy silane), aminopropyl tri(ethoxy silanes),-phenyl aminopropyl tri(ethoxy silane)), and other silane couplingagents, or mixtures thereof. In some embodiments, the final compositionis also thermoplastic (i.e., noncrosslinkable). Thus, in thesealternative embodiments, the composition will be essentially free (lessthan about 0.1% by weight and preferably about 0% by weight) ofcrosslinking agents, such as POWDERLINK™ by Cytec, and EPI-CURE™ 3200 byHexion Specialty Chemicals.

According to one aspect, the melt viscosity (complex coefficient ofviscosity) of the final composition will preferably be less than about100 Pa·S, more preferably less than about 50 Pa·S, and even morepreferably from about 1 Pa·S to about 35 Pa·S. For purposes of thesemeasurements, the melt viscosity is determined via rheological dynamicanalysis (TA Instruments, AR-2000, two parallel-plate configurationwhere the plates have a diameter of 25 mm). Furthermore, the meltviscosity is preferably determined at the preferred debondingtemperature of the composition in question. As used herein, the term“preferred debonding temperature” of the composition is defined as thetemperature at which the melt viscosity of the composition is below 100Pa·S, and is determined by dynamic measurement at 1 Hz oscillationfrequency in temperature ramp. The compositions also preferably have astorage modulus (G′) of less than about 100 Pa, preferably less thanabout 50 Pa, and even more preferably from about 1 Pa to about 26 Pa,when measured at the preferred debonding temperature of the composition.The storage modulus is determined by dynamic measurement at 1 Hzoscillation frequency in temperature ramp.

The compositions are thermally stable up to about 350° C. There is alsopreferably less than about 5% by weight, and more preferably less thanabout 1.5% by weight, loss of the composition after one hour at thepreferred debonding temperature plus 50° C. (preferably at a temperatureof from about 200° C. to about 300° C.), depending upon the composition.In other words, very little to no thermal decomposition occurs in thecomposition at this temperature, as determined by thermogravimetricanalysis (TGA), described herein.

Although the composition could be applied to either the carriersubstrate or active wafer first, it is preferred that it be applied tothe active wafer first. These compositions can be coated to obtainvoid-free thick films required for bump wafer applications and toachieve the required uniformity across the wafer. A preferredapplication method involves spin-coating the composition at spin speedsof from about 500-5000 rpm (more preferably from about 1000-3500 rpm),at accelerations of from about 3000-10,000 rpm/second, and for spintimes of from about 30-180 seconds. It will be appreciated that theapplication steps can be varied to achieve a particular thickness.

After coating, the substrate can be baked (e.g., on a hot plate) toevaporate the solvents. Typical baking would be at temperatures of fromabout 70-250° C., and preferably from about 80-240 ° C. for a timeperiod of from about 1-60 minutes, and more preferably from about 2-10minutes. The film thickness (on top of the topography) after bake willtypically be at least about 1 μm, and more preferably from about 10-200μm.

After baking, the desired carrier wafer is contacted with, and pressedagainst, the layer of inventive composition. The carrier wafer is bondedto this inventive composition by heating at a temperature of from about100-300° C., and preferably from about 120-180° C. This heating ispreferably carried out under vacuum and for a time period of from about1-10 minutes, under a bond force of from about 0.1 to about 25kiloNewtons. The bonded wafer can be subjected to backgrinding,metallization, patterning, passivation, via forming, and/or otherprocessing steps involved in wafer thinning, as explained in more detailbelow.

FIG. 1( a) illustrates an exemplary stack 10 comprising active wafer 12and carrier wafer or substrate 14. It will be appreciated that stack 10is not shown to scale and has been exaggerated for the purposes of thisillustration. Active wafer 12 has an active surface 18. As shown in FIG.1( a), active surface 18 can comprise various topographical features 20a-20 d. Typical active wafers 12 can include any microelectronicsubstrate. Examples of some possible active wafers 12 include thoseselected from the group consisting of microelectromechanical system(MEMS) devices, display devices, flexible substrates (e.g., cured epoxysubstrates, roll-up substrates that can be used to form maps), compoundsemiconductors, low k dielectric layers, dielectric layers (e.g.,silicon oxide, silicon nitride), ion implant layers, and substratescomprising silicon, aluminum, tungsten, tungsten silicide, galliumarsenide, germanium, tantalum, tantalum nitrite, SiGe, and mixtures ofthe foregoing.

Carrier substrate 14 has a bonding surface 22. Typical carriersubstrates 14 comprise a material selected from the group consisting ofsapphire, ceramic, glass, quartz, aluminum, silver, silicon,glass-ceramic composites (such as products sold under the name Zerodur®,available from Schott AG), and combinations thereof.

Wafer 12 and carrier substrate 14 are bonded together via bondingcomposition layer 24. Bonding layer 24 is formed of the cycloolefincopolymer compositions described above, and has been applied and driedas also described above. As shown in the FIG. 1( a), bonding layer 24 isbonded to active surface 18 of wafer 12 as well as to bonding surface 22of substrate 14. Unlike prior art tapes, bonding layer 24 is a uniform(chemically the same) material across its thickness. In other words, theentire bonding layer 24 is formed of the same composition.

It will be appreciated that, because bonding layer 24 can be applied toactive surface 18 by spin-coating or spray-coating, the bondingcomposition flows into and over the various topographical features.Furthermore, the bonding layer 24 forms a uniform layer over thetopography of active surface 18. To illustrate this point, FIG. 1 showsa plane designated by dashed line 26, at end portion 21 andsubstantially parallel to back surface 16. The distance from this planeto bonding surface 22 is represented by the thickness “T.” The thickness“T” will vary by less than about 20%, preferably by less than about 10%,more preferably by less than about 5%, even more preferably by less thanabout 2%, and most preferably less than about 1% across the length ofplane 26 and substrate 14.

The wafer package can then be subjected to subsequent thinning (or otherprocessing) of the substrate as shown in FIG. 1( b), where 12′ presentsthe wafer 12 after thinning. It will be appreciated that the substratescan be thinned to thicknesses of less than about 100 μm, preferably lessthan about 50 μm, and more preferably less than about 25 μm. Afterthinning, typical backside processing, including backgrinding,patterning (e.g., photolithography, via etching), passivation, andmetallization, and combinations thereof, may be performed.

Advantageously, the dried layers of the inventive compositions possess anumber of highly desirable properties. For example, the layers willexhibit low outgassing for vacuum etch processes. That is, if a 15-μmthick film of the composition is baked at 80-250° C. for 2-60 minutes(more preferably 2-4 minutes), the solvents will be driven from thecomposition so that subsequent baking at 140-300° C. for 2-4 minutesresults in a film thickness change of less than about 5%, preferablyless than about 2%, and even more preferably less than about 1.0% oreven 0% (referred to as the “Film Shrinkage Test”). Thus, the driedlayers can be heated to temperatures of up to about 350° C., preferablyup to about 320° C., more preferably up to about 300° C., withoutchemical reactions occurring in the layer. In some embodiments, thelayers can also be exposed to polar solvents (e.g.,N-methyl-2-pyrrolidone) at a temperature of 80° C. for 15 minuteswithout reacting.

The bond integrity of the dried layers can be maintained even uponexposure to an acid or base. That is, a dried layer of the compositionhaving a thickness of about 15 μm can be submerged in an acidic media(e.g., concentrated sulfuric acid) or base (e.g., 30 wt. % KOH) at 85°C. for about 45 minutes while maintaining bond integrity. Bond integritycan be evaluated by using a glass carrier substrate and visuallyobserving the bonding composition layer through the glass carriersubstrate to check for bubbles, voids, etc. Also, bond integrity ismaintained if the active wafer and carrier substrate cannot be separatedby hand.

After the desired processing has occurred, the active wafer or substratecan be separated from the carrier substrate. In one embodiment, theactive wafer and substrate are separated by heating to a temperaturesufficient to soften the bonding layer. More specifically, the stack isheated to temperatures of at least about 100° C., preferably at leastabout 120° C., and more preferably from about 150° C. to about 300° C.These temperature ranges represent the preferred debonding temperaturesof the bonding composition layer. This heating will cause the bondingcomposition layer to soften and form softened bonding composition layer24′ as shown in FIG. 1( c), at which point the two substrates can beseparated, for example, by sliding apart. FIG. 1( c) shows an axis 28,which passes through both of wafer 12 and substrate 14, and the slidingforces would be applied in a direction generally transverse to axis 28.Instead of sliding, wafer 12 or substrate 14 can be separated by liftingupward (i.e., in a direction that is generally away from the other ofwafer 12 or substrate 14) to separate the wafer 12 from the substrate14.

Alternatively, instead of heating to soften the layer, the bondingcomposition can be dissolved using a solvent. Once the layer isdissolved, the active wafer and substrate can be thereafter separated.Suitable solvents for use in dissolving the bonding layer can be anysolvent that was part of the composition prior to drying, such as thoseselected from the group consisting of MEK and cyclopentanone, as well ashydrocarbon solvents selected from the group consisting of limonene,mesitylene, dipentene, pinene, bicyclohexyl, cyclododecene,1-tert-butyl-3,5-dimethylbenzene, butylcyclohexane, cyclooctane,cycloheptane, cyclohexane, methylcyclohexane, and mixtures thereof.

Whether the bonding composition is softened or dissolved, it will beappreciated that separation can be accomplished by simply applying forceto slide and/or lift one of wafer 12 or substrate 14 while maintainingthe other in a substantially stationary position so as to resist thesliding or lifting force (e.g., by applying simultaneous opposingsliding or lifting forces to wafer 12 and substrate 14). This can all beaccomplished via conventional equipment.

Any bonding composition remaining in the device areas can be easilyremoved by rinsing with a suitable solvent followed by spin-drying.Suitable solvents include the original solvent that was part of thecomposition prior to drying as well as those solvents listed abovesuitable for dissolving the composition during debonding. Anycomposition remaining behind will be completely dissolved (at leastabout 98%, preferably at least about 99%, and more preferably about100%) after 5-15 minutes of exposure to the solvent. it is alsoacceptable to remove any remaining bonding composition using a plasmaetch, either alone or in combination with a solvent removal process.After this step, a clean, bonding composition-free wafer 12′ and carriersubstrate 14 (not shown in their clean state) will remain.

EXAMPLES

The following examples set forth preferred methods in accordance withthe invention. It is to be understood, however, that these examples areprovided by way of illustration and nothing therein should be taken as alimitation upon the overall scope of the invention.

Example 1 Cycloolefin Copolymer Resin and Low Molecular Weight COC ResinBlends

In this Example, formulations containing cycloolefin copolymers and alow molecular weight COC resin were made. Antioxidants were added tosome of the formulations.

1. Sample 1.1

In this procedure, 1.2 grams of an ethene-norbornene copolymer (TOPAS®5010, T_(g) 110° C.; obtained from TOPAS Advanced Polymers, Florence,Ky.) were dissolved in 6 grams of D-limonene (Florida Chemical Co.),along with 2.8 grams of a low molecular weight cycloolefin copolymer(TOPAS® Toner™, M_(w) 8,000, M_(w)/M_(n) 2.0). The solution was allowedto stir at room temperature until the ingredients were in solution. Thesolution had about 40% solids.

2. Sample 1.2

In this procedure, 0.75 grams of an ethene-norbornene copolymer (TOPAS®8007, T_(g) 78° C.) and 3.25 grams of low molecular weight COC (TOPAS®Toner™) were dissolved in 6 grams of D-limonene. The solution wasallowed to stir at room temperature until the ingredients were insolution. The solution had about 40% solids.

3. Sample 1.3

For this procedure, 1.519 grams of an ethene-norbornene copolymer(TOPAS® 5013, T_(g) 134° C.) were dissolved in 5.92 grams of D-limonenealong with 2.481 grams of a low molecular weight cycloolefin copolymer(TOPAS® Toner™), 0.04 grams of a phenolic antioxidant (IRGANOX® 1010),and 0.04 grams of a phosphonite antioxidant (IRGAFOX® P-EPQ). Thesolution was allowed to stir at room temperature until the ingredientswere in solution. The solution had about 40% solids.

4. Sample 1.4

In this procedure, 1.2 grams of an ethene-norbornene copolymer (TOPAS®8007) were dissolved in 5.92 grams of D-limonene along with 2.8 grams ofa low molecular weight cycloolefin copolymer (TOPAS® Toner™), 0.04 gramsof a phenolic antioxidant (IRGANOX® 1010), and 0.04 grams of aphosphonite antioxidant (IRGAFOX® P-EPQ). The solution was allowed tostir at room temperature until the ingredients were in solution. Thesolution had about 40% solids.

5. Sample 1.5

For this procedure, 2.365 grams of an ethene-norbornene copolymer(TOPAS® 5013) were dissolved in 5.92 grams of D-limonene along with1.635 grams of a low molecular weight cycloolefin copolymer (TOPAS®Toner™), 0.04 grams of a phenolic antioxidant (IRGANOX® 1010), and 0.04grams of a phosphonite antioxidant (IRGAFOX® P-EPQ). The solution wasallowed to stir at room temperature until the ingredients were insolution. The solution had about 40% solids.

6. Sample 1.6

In this procedure, 2.2 grams of a hydrogenated norbornene-basedcopolymer prepared by ring-opening polymerization (ZEONOR® 1060, T_(g)100° C.; obtained from Zeon Chemicals, Louisville, Ky.) and 1.8 grams ofa low molecular weight cycloolefin copolymer (TOPAS® Toner™) weredissolved in 5.92 grams of cyclooctane (Aldrich, Milwaukee, Wis.). Thesolution was allowed to stir at room temperature until the ingredientswere in solution. The solution had about 40% solids.

Example 2

Cycloolefin Copolymer Resins and Tackifier Blends

In this Example, formulations were made containing cycloolefincopolymers blended with various tackifiers. As in Example 1,antioxidants were added to some of the formulations.

1. Sample 2.1

In this procedure, 0.83 grams of an ethene-norbornene copolymer (TOPAS®8007) were dissolved in 5.92 grams of D-limonene, along with 3.17 gramsof a hydrogenated hydrocarbon resin (REGALITE® R1125; obtained fromEastman Chemical Co., Kingsport Tenn.), 0.04 grams of a phenolicantioxidant (IRGANOX® 1010), and 0.04 grams of a phosphonite antioxidant(IRGAFOX® P-EPQ). The solution was allowed to stir at room temperatureuntil the ingredients were in solution. The solution had about 40%solids.

2. Sample 2.2

For this procedure, 0.7 grams of an ethene-norbornene copolymer (TOPAS®8007) and 3.3 grams of a styrenated terpene resin (ZONATAC® NG98;obtained from Arizona Chemical, Jacksonville, Fla.) were dissolved in5.92 grams of D-limonene, along with 0.04 grams of a phenolicantioxidant (IRGANOX® 1010), and 0.04 grams of a phosphonite antioxidant(IRGAFOX® P-EPQ). The solution was allowed to stir at room temperatureuntil the ingredients were in solution. The solution had about 40%solids.

3. Sample 2.3

In this formulation, 1.9 grams of an ethene-norbornene copolymer (TOPAS®5013) were dissolved in 5.92 grams of D-limonene, along with 2.1 gramsof a cyclo-aliphatic hydrocarbon resin (ARKON® P-140; obtained fromArakawa Chemical USA Inc., Chicago, Ill.), 0.04 grams of a phenolicantioxidant (IRGANOX® 1010), and 0.04 grams of a phosphonite antioxidant(IRGAFOX® P-EPQ). The solution was allowed to stir at room temperatureuntil the ingredients were in solution.

4. Sample 2.4

For this procedure, 2.42 grams of an ethene-norbornene copolymer (TOPAS®5013) were dissolved in 5.92 grams of D-limonene, along with 1.58 gramsof a cyclo-aliphatic hydrocarbon resin (PLASTOLYN® R-1140; obtained fromArakawa Chemical USA Inc., Chicago, Ill.), 0.04 grams of a phenolicantioxidant (IRGANOX® 1010), and 0.04 grams of a phosphonite antioxidant(IRGAFOX® P-EPQ). The solution was allowed to stir at room temperatureuntil the ingredients were in solution. The solution had about 40%solids.

Example 3

Application, Bonding and Debonding, and Analysis

The formulations prepared in Examples 1 and 2 above were spin-coatedonto various substrate wafers. After baking to evaporate the solvent andallowing the bonding composition to reflow, a second wafer was bonded toeach coated wafer by applying pressure. A typical procedure fortemporary wafer bonding using the bonding compositions is illustrated inFIG. 2. The bonded wafers were tested for mechanical strength, thermalstability, and chemical resistance. The wafers were tested for debondingby manually sliding them apart at acceptable temperatures. Afterdebonding, the bonding composition residue was cleaned using a solventrinse and spinning.

The rheological properties of each formulation from Examples 1 and 2were tested. All of these materials were successfully tested fordebonding. It was determined that the preferred debonding temperaturefor samples 1.1, 1.2, 2.1, and 2.2 was 150° C. The preferred debondingtemperature for samples 1.3, 1.4, and 2.3 was 200° C., and the preferreddebonding temperature for samples 1.5, 1.6, and 2.4 was 250° C. Thestorage modulus (G′) and melt viscosity (η*, complex coefficient ofviscosity) for each sample at their preferred debonding temperatures arereported below. The theological data is also illustrated in FIGS. 3-5for each debonding temperature.

TABLE 1 Sample Storage Modulus, G′ Viscosity, η* Debonding number (Pa)(Pa · s) Temperature (° C.) 1.1 25.5 35.0 150 1.2 9.6 16.7 150 1.3 8.013.9 200 1.4 3.5 5.1 200 1.5 16.3 20.1 250 1.6 8.1 15.1 250 2.1 24.914.5 150 2.2 1.3 2.4 150 2.3 21.7 28.7 200 2.4 5.5 14.1 250

Further studies on thermal stability and chemical resistance were alsocarried out on these compositions. Thermogravimetric analysis (TGA) wascarried out on a TA Instruments thermogravimetric analyzer. The TGAsamples were obtained by scraping off the spin-coated and baked bondingcomposition samples from Examples 1 and 2. For the isothermal TGAmeasurement, the samples were heated in nitrogen at a rate of 10°C./min., up to their preferred debonding temperature plus 50° C., andkept constant at that temperature for 1 hour to determine the thermalstability of the particular bonding composition. The isothermalmeasurements for each sample formulation are reported below in Table 2.For the scanning TGA measurement, the samples were heated in nitrogen ata rate of 10° C./min. from room temperature to 650° C.

TABLE 2 Isothermal thermogravimetric results - thermal stability (in N₂)Weight Loss (%) Isothermal temperature Sample (Isothermal for 1 hour) (°C.) 1.1 0.123 200 1.2 0.847 200 1.3 1.268 250 1.4 0.764 250 1.5 0.752300 1.6 0.596 300 2.1 5.496 200 2.2 4.650 200 2.3 5.737 250 2.4 5.191300

As can be seen from the Table above, all of the COC-low molecular weightCOC resin blends (Example 1) possessed the required thermal stability atleast up to 300° C. and exhibited minimal weight loss (<1.5-wt %). TheCOC-tackifier blends (Example 2) had an average weight loss of about5-wt % when maintained at the testing temperature. However, as shown inTable 3, below, the 1-wt % weight loss temperatures were higher thantheir respective bonding/debonding temperatures, suggesting sufficientthermal resistance for wafer-bonding applications.

TABLE 3 Scanning thermogravimetric results Temperature at 1.0% weightloss Debonding Temperature Sample (° C.) (° C.) 2.1 214 150 2.2 223 1502.3 228 200 2.4 252 250

To determine chemical resistance, two silicon wafers were bonded usingthe particular bonding composition to be tested. The bonded wafers wereput into chemical baths of N-Methyl-2-Pyrrolidone (NMP) or 30% by weightKOH at 85° C., and concentrated sulfuric acid at room temperature todetermine chemical resistance. The bond integrity was visually observedafter 45 minutes, and the stability of the bonding composition againstthe respective chemical was determined. All bonding compositionsretained the bond integrity.

1. A wafer bonding method comprising: providing a stack comprising firstand second substrates bonded together via a bonding layer, said layerbeing formed from a composition comprising a cycloolefin copolymerdissolved or dispersed in a solvent system; and separating said firstand second substrates.
 2. The method of claim 1, further comprisingsubjecting said stack to a temperature at least about 100° C. to softensaid bonding layer prior to said separating.
 3. The method of claim 1,further comprising dissolving said bonding layer with a solvent prior tosaid separating.
 4. The method of claim 3, said solvent being selectedfrom the group consisting of limonene, mesitylene, dipentene, pinene,bicyclohexyl, cyclododecene, 1-tert-butyl-3,5-dimethylbenzene,butylcyclohexane, cyclooctane, cycloheptane, cyclohexane,methylcyclohexane, methyl ethyl ketone, cyclopentanone, and mixturesthereof.
 5. The method of claim 1, wherein said separating comprisesapplying a force to at least one of said first and second substrateswhile causing the other of said first and second substrates to resistsaid force, said force being applied in a sufficient amount so as toseparate said first and second substrates.
 6. The method of claim 1,further comprising subjecting said stack to a process selected from thegroup consisting of backgrinding, metallizing, patterning, passivation,and combinations thereof, prior to said separating.
 7. The method ofclaim 1, wherein said providing a stack comprises: applying a bondingcomposition to at least one of the first and second substrates; andcontacting the substrates with one another so as to bond the substratestogether.
 8. The method of claim 1, wherein: said first substrate has afirst surface and a second surface remote from said first surface andcomprising at least one active site and plurality of topographicalfeatures, and said bonding composition layer is bonded to said secondsurface; and said second substrate comprises a bonding surface that isbonded to said bonding composition layer.
 9. The method of claim 8,wherein: said topographical features present respective end surfacesremote from the first surface of said first substrate, and at least oneof the end surfaces is further from the first surface of the firstsubstrate than the other of said end surfaces, said further end surfacedefining a plane that is substantially parallel to said first surface;and the distance from said plane to the bonding surface on said secondsubstrate varying by less than about 20% across said plane and secondsubstrate bonding surface.
 10. The method of claim 1, said compositionfurther comprising an ingredient selected from the group consisting oftackifiers, low molecular weight cycloolefin copolymers, plasticizers,antioxidants, and mixtures thereof.
 11. The method of claim 1, whereinsaid copolymer is formed from the polymerization of a cyclic olefinselected from the group consisting of

and combinations of the foregoing, where: each R₁ and R₂ is individuallyselected from the group consisting of —H, and alkyl groups; and each R₃is individually selected from the group consisting of —H, substitutedand unsubstituted aryl groups, alkyl groups, cycloalkyl groups, aralkylgroups, ester groups, ether groups, acetyl groups, alcohols, aldehydegroups, ketones, nitriles, and combinations thereof.
 12. The method ofclaim 1, wherein said copolymer comprises recurring monomers of:

and combinations of the foregoing, where: each R₁ and R₂ is individuallyselected from the group consisting of —H, and alkyl groups; and each R₃is individually selected from the group consisting of —H, substitutedand unsubstituted aryl groups, alkyl groups, cycloalkyl groups, aralkylgroups, ester groups, ether groups, acetyl groups, alcohols, aldehydegroups, ketones, nitriles, and combinations thereof; and

where:

is a single or double-bond; and each R₄ is individually selected fromthe group consisting of —H and alkyl groups.
 13. An article comprising:a first substrate having a back surface and an active surface, saidactive surface comprising at least one active site and a plurality oftopography features; a second substrate having a bonding surface; and abonding layer bonded to said active surface and to said bonding surface,wherein said bonding layer is formed from a composition comprising acycloolefin copolymer dissolved or dispersed in a solvent system. 14.The article of claim 13, wherein: said topographical features presentrespective end surfaces remote from the back surface of said firstsubstrate, and at least one of the end surfaces is further from the backsurface of the first substrate than the other of said end surfaces, saidfurther end surface defining a plane that is substantially parallel tosaid first surface; and the distance from said plane to the bondingsurface on said second substrate varying by less than about 20% alongsaid plane and second substrate bonding surface.
 15. The article ofclaim 13, wherein said first substrate is selected from the groupconsisting of microelectromechanical system devices, display devices,flexible substrates, compound semiconductors, low k dielectric layers,dielectric layers, ion implant layers, and substrates comprisingsilicon, aluminum, tungsten, tungsten silicide, gallium arsenide,germanium, tantalum, tantalum nitrite, SiGe, and mixtures of theforegoing.
 16. The article of claim 13, wherein said second substratecomprises a material selected from the group consisting of sapphire,ceramic, glass, quartz, aluminum, silver, silicon, glass-ceramiccomposites, and combinations thereof.
 17. The article of claim 13,wherein said copolymer is formed from the polymerization of a cyclicolefin selected from the group consisting of

and combinations of the foregoing, where: each R₁ and R₂ is individuallyselected from the group consisting of —H, and alkyl groups; and R₃ isindividually selected from the group consisting of —H, substituted andunsubstituted aryl groups, alkyl groups, cycloalkyl groups, aralkylgroups, ester groups, ether groups, acetyl groups, alcohols, aldehydegroups, ketones, nitriles, and combinations thereof.
 18. The article ofclaim 13, wherein copolymer comprises recurring monomers of:

and combinations of the foregoing, where: each R₁ and R₂ is individuallyselected from the group consisting of —H, and alkyl groups; and each R₃is individually selected from the group consisting of —H, substitutedand unsubstituted aryl groups, alkyl groups, cycloalkyl groups, aralkylgroups, ester groups, ether groups, acetyl groups, alcohols, aldehydegroups, ketones, nitriles, and combinations thereof, and

where:

is a single or double-bond; and each R₄ is individually selected fromthe group consisting of —H and alkyl groups.
 19. The article of claim13, said composition further comprising an ingredient selected from thegroup consisting of tackifiers, low molecular weight cycloolefincopolymers, plasticizers, antioxidants, and mixtures thereof.
 20. Thearticle of claim 19, wherein said ingredient is a tackifier selectedfrom the group consisting of polyterpene resins, beta-polyterpeneresins, styrenated terpene resins, polymerized rosin resins, rosin esterresins, cyclo-aliphatic hydrocarbon resins, C5 aliphatic hydrocarbonresins, hydrogenated hydrocarbon resins, and mixtures thereof.
 21. Thearticle of claim 19, wherein said ingredient is a low molecular weightcycloolefin copolymer having a weight average molecular weight of lessthan about 50,000 Daltons.
 22. A composition useful for bonding twosubstrates together, said composition comprising a cycloolefin copolymerand an ingredient dissolved or dispersed in a solvent system, saidingredient being selected from the group consisting of tackifier resins,low molecular weight cycloolefin copolymers, and mixtures thereof 23.The composition of claim 22, said composition comprising from about 5%to about 85% by weight of said copolymer, based upon the total weight ofthe composition taken as 100% by weight.
 24. The composition of claim22, wherein said solvent system is selected from the group consisting oflimonene, mesitylene, dipentene, pinene, bicyclohexyl, cyclododecene,1-tert-butyl-3,5-dimethylbenzene, butylcyclohexanc, cyclooctane,cycloheptane, cyclohexane, methylcyclohexane, methyl ethyl ketone,cyclopentanone, and mixtures thereof.
 25. The composition of claim 22,said copolymer being formed from the polymerization of a cyclic olefinselected from the group consisting of

and combinations of the foregoing, where: each R₁ and R₂ is individuallyselected from the group consisting of —H, and alkyl groups; and each R₃is individually selected from the group consisting of —H, substitutedand unsubstituted aryl groups, alkyl groups, cycloalkyl groups, aralkylgroups, ester groups, ether groups, acetyl groups, alcohols, aldehydegroups, ketones, nitriles, and combinations thereof.
 26. The compositionof claim 25, wherein said cyclic olefin is polymerized with an acyclicolefin selected from the group consisting of branched and unbranchedC₂-C₂₀ alkenes.
 27. The composition of claim 22, wherein said copolymercomprises recurring monomers of:

and combinations of the foregoing, where: each R₁ and R₂ is individuallyselected from the group consisting of —H, and alkyl groups; and each R₃is individually selected from the group consisting of —H, substitutedand unsubstituted aryl groups, alkyl groups, cycloalkyl groups, aralkylgroups, ester groups, ether groups, acetyl groups, alcohols, aldehydegroups, ketones, nitriles, and combinations thereof; and

where:

is a single or double-bond; and each R₄ is individually selected fromthe group consisting of —H and alkyl groups.
 28. The composition ofclaim 22, where said ingredient is present in said composition at alevel of from about 2% to about 80% by weight, based upon the totalweight of the composition taken as 100% by weight.
 29. The compositionof claim 22, wherein said ingredient is a tackifier resin selected fromthe group consisting of polyterpene resins, beta-polyterpene resins,styrenated terpene resins, polymerized rosin resins, rosin ester resins,cyclo-aliphatic hydrocarbon resins, C5 aliphatic hydrocarbon resins,hydrogenated hydrocarbon resins, and mixtures thereof.
 30. Thecomposition of claim 22, wherein said ingredient is a low molecularweight cycloolefin copolymer having a weight average molecular weight ofless than about 50,000 Daltons.
 31. The composition of claim 22, whereinsaid composition is essentially free of adhesion promoting agents. 32.The composition of claim 22, said composition having thermal stabilityup to a temperature of about 350° C.
 33. The composition of claim 22,said composition being essentially free of crosslinking agents.
 34. Thecomposition of claim 22, said composition further comprising anantioxidant selected from the group consisting of phenolic antioxidants,phosphite antioxidants, phosphonite antioxidants, and mixtures thereof.35. The composition of claim 22, said composition having a meltviscosity of less than about 100 Pa·S at the debonding temperature ofsaid composition.